1. Field of the Invention
This invention relates to a magnetic recording disk cartridge, and more particularly to a magnetic recording disk cartridge comprising a magnetic recording disk having a center core and accommodated for rotation in a casing.
2. Description of the Prior Art
There has been in wide use, as a recording medium for computers, a floppy disk which comprises a magnetic recording disk consisting of a disk-like flexible base sheet formed of polyester resin and a magnetic material layer formed on each side of the base sheet. Information is recorded on the magnetic material layer by a magnetic head while the floppy disk is rotated.
Further, there has been put into practical use an electronic still camera in which a smaller floppy disk is used as a recording medium for recording images. The magnetic recording disk for the electronic still camera is small in diameter and extremely thin, and is provided with a center core fixed to the center of the base sheet. The magnetic recording disk is accommodated for rotation in a small casing to form a magnetic recording disk cartridge.
The center core of the magnetic recording disk is provided with a central opening into which a spindle of an electronic still camera, a reproducing system or the like is fitted to rotate the magnetic recording disk at a high speed. In order to precisely record image information on the magnetic recording disk, the center of the magnetic recording disk must coincide with the rotational axis of the spindle.
Conventionally, the spindle is brought into contact with the wall of the center core defining the central opening at a plurality of portions and one of the plurality of portions of the wall is in the form of a thin plate that has resiliency. The center core is molded in one piece of a resin material. When the spindle is fitted into the central opening, the thin plate is resiliently deformed and the outer peripheral surface of the spindle is urged radially inwardly by the resiliency of the thin plate so that the spindle is positioned in place with respect to the central opening of the center core, so that the spindle and the magnetic recording disk are coaxial with each other.
However, the conventional center core structure is disadvantageous in that when the thickness of the thin plate portion is reduced in order to provide sufficient flexibility, the moldability of the center core is lowered and the resilient force of the thin plate portion is weakened. Further, as it is formed of resin material, the center core has poor thermal resistance and durability. Thus, the conventional center core is not satisfactory as means for locating the spindle with respect to the magnetic recording disk.